1. Field of the Invention
The present invention relates to peptides activating a cancer-related gene and derived from cell membrane surfaces of human cancer cells, immunosuppressive agents including the peptides as an effective component, and anticancer agents including antibodies against the peptides as an effective component. The present invention further relates to diagnostic reagents including polynucleotides encoding the peptides for diagnosing malignancy of cancer or tendency of canceration. Furthermore, the present invention relates to methods for manufacturing the peptides.
2. Description of the Related Art
Cancer is a disease caused by cells which started unregulated growth. The cells continue to proliferate and infiltrate into neighboring normal cells to destroy the normal functions. Some of the cells spread by metastasis from their original site to one or more sites elsewhere in the body, leading to a loss of normal cell functions and to depression of functions of organs. Thus, cancer is a disease that leads patients to death. Normal cells proliferate but will stop growing when they come in contact with solid substances (contact inhibition). On the other hand, the contact inhibition property is lost in cancerous cells. Consequently, the cancerous cells continue to grow in their host as long as the host is alive. Among cells extracted from the body, cells having ability for continuing unlimited growth can be established as a cell line. Cancer, in a broad sense, is a state of uncontrolled cell growth due to mutation of a gene, in particular, due to mutation of a gene positively or negatively regulating cell growth. Heretofore, many studies have been conducted on genes contributing to carcinogenesis or a growth mechanism and peptides or proteins relating to them (Japanese Unexamined Patent Application Publication Nos. 2003-517306 and 2000-217585).
Among peptides or proteins derived from cell membrane surfaces of human cancer cells, generally, HLA-binding peptides are particularly thought to be cancer antigens and are thought to act on immunocompetent cells as antigens, most of all, as immunogens. Additionally, it is widely known that some proteins and glycoproteins derived from cancer cells and immunocompetent cells such as macrophages isolated from a cancer-bearing living body have an immunosuppressing activity preventing the destruction of cancer cells, for example, immunosuppressive acidic protein (IAP). Such proteins and glycoproteins are clinically used for measuring the degree of immunosuppression.
Heretofore, it has been thought that cancer cell growth progresses by a mechanism due only to self division of cancerous cells. However, the rate of cancer cell growth is not constant and cancer cells rapidly proliferate at some point. Such phenomena cannot be fully explained by the conventional view only.